Fix some Windows warnings

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=3980

Change-Id: Icfc5dfb985b966c625d9bc81f61719ac5549085e
Reviewed-on: https://skia-review.googlesource.com/3980
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
diff --git a/third_party/gif/SkGifImageReader.h b/third_party/gif/SkGifImageReader.h
index 09c5622..45a1ce6 100644
--- a/third_party/gif/SkGifImageReader.h
+++ b/third_party/gif/SkGifImageReader.h
@@ -110,7 +110,7 @@
     bool prepareToDecode();
     bool outputRow(const unsigned char* rowBegin);
     bool doLZW(const unsigned char* block, size_t bytesInBlock);
-    bool hasRemainingRows() { return rowsRemaining; }
+    bool hasRemainingRows() { return SkToBool(rowsRemaining); }
 
 private:
     // LZW decoding states and output states.